No-bounce tailgate assembly

ABSTRACT

In a tailgate assembly, a locking mechanism for preventing rotation of the assembly in response to a torque generated by a moment arm of the tailgate assembly and a force resulting from the jolting of the truck as it travels over rough terrain.

RELATED APPLICATIONS

This application is a continuation of copending application Ser. No.544,041, filed on Jun. 26, 1990, (now abandoned) which is a continuationof application Ser. No. 309,025, filed on Feb. 6, 1989 (now abandoned),which is a continuation of application Ser. No. 071,816, filed on Jul.10, 1987(now abandoned).

TECHNICAL FIELD

The invention generally relates to tailgate assemblies for off-road,heavy-duty trucks and more particularly relates to mechanisms forraising and lowering tailgates.

BACKGROUND

Because tailgate assemblies can be damaged by the difficult tasksperformed by off-road, heavy-duty trucks, the bodies of the trucks havetraditionally been designed to function without tailgates. But, as aresult of a desire to increase capacity, tailgate assemblies have beendesigned which are capable of withstanding the harsh working environmentof off-road trucks. For example, in U.S. Pat. No. 3,751,112 to Hagenbucha tailgate assembly includes two side plates that are pivotallyconnected to the sides of the body. In order to raise the tailgate uponthe pivoting of the body, a pair of outriggers mounted to the frame ofthe truck, secure one end of a pair of chains (or cables) which causethe tailgate to rotate when the body is dumped.

By providing outriggers, the chains or cables which rotate the tailgateare attached at a point on the frame which extends out beyond the sideof the body. By attaching one end of the chains at the end of theoutriggers, the chains are not biased around the bottom edge of thebody, which would cause damage to both the chains and the truck body.

But, because the outriggers are a cantilever and extend from the frameto a point beyond the sides of the body, the outriggers may be plaguedwith problems under certain conditions. For instance, because of limitedavailable space on the frames of some truck models, the area of the baseof the outriggers (where they attach to the frame) may be smaller thandesired. The strength of the outriggers may be compromised if the basesof the outriggers have areas too small for the outriggers to withstandthe forces exerted at the ends of the outriggers as the tailgate isrotated when the body pivots. As a result of the area of the base beingtoo small, the outriggers may be susceptible to bending after repeateduse. Finally, some manufacturers of trucks are reluctant to honorwarranties if the frame of the truck has been subjected to welding as isrequired to mount the outriggers for the addition of a tailgateassembly.

One attempt at eliminating the potential problems of the use ofoutriggers to raise tailgates has been to use a shortened outriggerwhich does not extend beyond the sides of the body. By shortening theoutrigger, the weakening caused by cantilevering is reduced. Becausethese outriggers do not extend beyond the sides of the body, the chains(or cables) are biased against the bottom edge of the body. When thebody is pivoted to a dump position, the chains move relative to thebottom edge of the body. In order to prevent damage of the body or thechains as the body pivots in dumping, an elongated roller is mounted oneach side of the body in order to protect the truck body and reduce wearof the chain.

Each roller is elongated because, as the body pivots, the chain changesposition along the length of the sides of the body. As a result, inaddition to the roller rotating as the chain pulls the tailgate to araised position, the chain also walks along the length of the roller asthe relative positions of the chain and roller change. Because offrictional forces, the chain does not walk smoothly along the length ofthe roller; instead, it moves in a jerking motion caused by the frictionbetween the roller and chain holding the chain in a stationary lateralposition until movement of the body and tailgate cause an angle in thechain which creates sufficient force to overcome the friction. As thebody continues to pivot, the forces created by the bending chainincrease until they again overcome the friction and the chain snaps to anew position. This jerking movement is extremely hard on both therollers, the chains, the outrigger, the tailgate and the truck frame. Asa result, the rollers and chains wear out quickly.

To overcome the foregoing wear problem, it is known to use a cableconnection instead of a chain. Because a cable is composed of multiplestrands of wire, frictional forces between strands become substantial ifthe elongated rollers bend the cable at too great an angle. In order toreduce the angle, the shortened outriggers are provided. Although theamount of extension of these shortened outriggers reduces problemsinherent in a cantilevered support off the truck frame, the problemsremain.

A related problem of tailgate assemblies that often causes damage is theundesirable "bouncing" or rotation of the assembly in response to atorque created about the tailgate's rotational axis by a moment armbetween the rear axle of the truck and the tailgate's center of gravitycreated in response to oscillation of the rear axle relative to thesurface of the road. This bouncing or banging of the tailgate assemblyon the body of the truck may cause damage, depending on the length ofthe moment arm and the condition of the road. For truck bodies thatextend substantially beyond the rear axle of the truck, the lever arm issufficiently great that even relatively smooth roads will cause bangingof the tailgate assembly that may be damaging.

SUMMARY OF THE INVENTION

The primary objective of the invention is to provide a tailgate assemblythat is immune from the rotational effects resulting from jolting of thetruck as it travels over rough terrain.

Other objects and advantages will become apparent with reference to thefollowing detailed description when taken in conjunction with thedrawings.

The invention provides a locking mechanism for the tailgate of adump-body truck that prevents uncontrolled rotation of the tailgate inresponse to jolting of the truck as it travels over rough roads or thelike. The locking mechanism is responsive to rotation of the dump bodyfor unlocking the tailgate from the body, thereby allowing the tailgateto be controllably rotated to an out-of-the-way position.

While the invention will be described in some detail with reference to apreferred embodiment, it is to be understood that it is not intended tolimit the invention to such detail. On the contrary, it is intended tocover all alternatives, modifications and equivalents which fall withinthe spirit and scope of the invention as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heavy-duty, off-road truck with thebody of the truck in its fully pivoted position in order to most clearlyshow the connecting mechanism for raising and lowering the tailgateassembly of the body;

FIG. 2 is a side view of the truck showing the body in its fully loweredposition in order to illustrate the position of a chain in a rollerassembly of the connecting mechanism;

FIG. 3 is a rear view of the truck showing the body in its fully loweredposition, taken along the line 3--3 in FIG. 2;

FIG. 4 is a side view of the body of the truck in a full pivotedposition illustrating the position of the chain of the connectingmechanism of the invention compare to its position when the body isfully lowered as shown in FIGS. 2 and 3;

FIG. 5 is a front view of the fully pivoted body taken along the line5--5 in FIG. 4;

FIG. 6 is an enlarged perspective view of one of the two rollerassemblies of the connecting mechanism with a portion of the assemblycut away to more clearly illustrate the relative positions of the pairof rollers in the assembly;

FIG. 7 is a side view of a heavy-duty, off-road truck, having theconnecting mechanisms and including a locking mechanism according to theinvention that eliminates uncontrolled rotation of the tailgateassembly;

FIG. 8 is a side view of the truck shown in FIG. 7 with the bodyslightly rotated about its pivot axis in order to indicate the movementof the tailgate caused by the connecting mechanism in response to theinitial rotation of the body;

FIG. 9 is a side view of the truck shown in FIGS. 7 and 8 with the bodyrotated into its fully raised position in order to illustrate the fullyopened position of the tailgate assembly;

FIG. 10 is an enlarged and partial side view of the rear portion of thetruck body in FIG. 7, illustrating in phantom line the position of thelocking mechanism of the invention for latching a rear panel of thetailgate assembly to side panels of the assembly and to the body of thetruck;

FIG. 11 is an enlarged and partial side view of the rear portion of thetruck body in FIG. 8, illustrating in phantom line the position of thelocking mechanism as it responds to the rotation of the truck body inorder to free the lower portion of the back panel of the tailgateassembly and allow rotation of the panel about an axis of rotationorthogonal to the two, parallel side panels of the tailgate assembly;

FIG. 12 is an enlarged and partial side view of the back portion of thetruck body in FIG. 9, illustrating in phantom line the position of theback panel and its locking mechanism when the truck body is in its fullyraised position;

FIG. 13 is an enlarged partial view of the rear portion of the tailgateassembly with the outside plate of the side panel removed in order toexpose the locking mechanism for the back panel;

FIG. 14 is a plan view of the rear portion of the truck body andtailgate assembly; and

FIG. 15 is an enlarged plan view of a corner of the tailgate assembly,partially cut away to expose the locking mechanism for latching the rearback of the tailgate assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown the typical rear dump vehicleillustrated in the dump position. The rear dump vehicle includes a dumpbody 11 having a pair of side sheets 13 (one sheet shown only), a frontsheet 15 and a bottom sheet 17. Furthermore, some rear dump vehiclesinclude a canopy 19 coupled to the dump body 11. The canopy operates toprotect a cab 21 when the rear dump vehicle is being loaded. The sidesheets 13, the front sheet 15 and the bottom sheet 17 provide an opentop wherein earth or other loaded material can be inserted in the dumpbody 11. The dump body 11 is generally connected to the main frame 23 bya body pivot assembly 25 so that the body can be rotated about a bodypivot pin 25a for dumping the load.

A tailgate assembly 27 is illustrated having a pair of side plates 29(one of which is illustrated only) and a rear plate 31. The side plates29 are pivotally connected to the side sheets 13 of the dump body 11 bya tailgate pivot pin 33. Consequently, the tailgate 27 can pivot aboutthe pivot pin 33 to provide both a dump position (as shown in FIG. 1)and a load position (as shown in FIG. 2). The rear plate 31 of thetailgate 27 is illustrated in FIG. 2 as extending beyond the rearportions of the side sheets 13. Furthermore, the rear plate 31 is shownsubstantially perpendicular to a ground surface. Consequently, the rearplate 31 when in the load position provides an increased volume for thedump body 11 in which loaded material can be placed.

The forward edge of the side plates 29 of the tailgate assembly 27 haveextension pieces 35 thereon which provide an anchor for a chain 37. Atthe opposite end of the chain 37, it is connected to an elongatedmounting support 39. The mounting support 39 is in turn connected (e.g.,bolted) to a base section 40 for the hoist cylinders 42. As an aid indescribing relative movement of the dump body 11, the tailgate assembly27 and the chain 37, a Cartesian coordinate system is illustrated with aY-axis aligned parallel with the axis of rotation for the dump body andthe X-axis parallel with the length of the vehicle. The Z-axis issubstantially vertical with respect to the ground.

As the forward portion of the dump body 11 is raised by the hoistcylinders 42, the dump body is pivoted about the body pivot pin 25a.Pivoting of the dump body 11 causes the chain 37 to become taut and, asa result, exerts a torque on the side plate 29 which causescounterclockwise rotation of the tailgate assembly 27 about the pivotpin 33. As illustrated in FIG. 1, pivoting of the dump body 11 causesthe rear plate 31 to rotate to a position which substantially clears thenormal maximum load height of loaded material carried in the dump body.Consequently, any material on the bottom sheet 17 of the dump body 11can be discharged beneath the rear plate 31 of the tailgate assembly 27and through the rear portion of the side sheets 13.

The tailgate pivot pin 33 can be located at any desired positionrelative to the side plate 29 of the tailgate assembly 27 and the sidesheets 13 of the dump body 11. However, a desired position for thetailgate pivot pin 33 is in a position which causes a slight raising ofthe rear plate 31 of the tailgate assembly 27 to an angle approximately90° between the top of side sheets 13 and the top of side plate 29. Aslight raising of the rear plate 31 provides increased clearance betweenthe rear plate and the bottom sheet 17 for discharge of the loadedmaterial. By placing the pivot pin 33 substantially forward from therear of the side sheets 13 (as shown in FIG. 1), rotating motion of thesurface of the rear plate 31 is upwardly and over the loaded material.

The mounting support 39 is preferably an elongated, square and hollowtubing (e.g., steel) which is secured to the lowermost portion of thebase section 40 which anchors one end of each of the hoist cylinders 42.Although the mounting support 39 eliminates the need for outriggers, thechain 37 can no longer maintain a straight line in the Y-Z plane, as itcould when an outrigger was present.

As best seen in FIG. 3, a straight line SL in the Y-Z plane connectingthe extension piece 35 to the end 39a of the mounting support 39 cutsthrough the side walls 13 and the bottom 17. Therefore, the chain 37must be biased around the edge 41 formed where the side 13 meets thebottom 17. In order to direct the chains 37 around their respectiveedges 41, a pair of roller assemblies 43 are mounted (e.g., welded) onthe bottom sheet 17 and adjacent the edges 41 in order to engage thechains 37 and prevent scraping of the edges against the chains as theymove relative to one another as the dump body 11 pivots.

Referring more particularly to FIGS. 2 and 3, in the lowered position ofthe dump body 11, each of the chains 37 describe a generally straightline in the X-Z plane (depending on the precise position of the rollerassemblies 43) and an angled line in the Y-Z plane. The angling of thechain 37 in the Y-Z plane is provided by a cylindrical roller 45 in eachof the roller assemblies 43 which causes the chain to be biased awayfrom the edge 41. Because the roller 45 is mounted for rotation about anaxis r₁ which is substantially transverse to the line formed by thechain 37 in the X-Z plane, pivoting of the dump body 11 will cause theroller 45 to rotate as the chain moves over the surface of the roller.

Each of the roller assemblies includes a second roller whose axis ofrotation is approximately transverse to that of roller 45; when thechain is biased away from the edge 41 in the Y-Z plane by the roller 45during pivoting of the dump body 11 and rotation of the tailgateassembly 27, the chain also is biased forward in the X-Z plane by thesecond roller so that the sliding of the chain along the length of theroller 45 is limited. Each of the second rollers is mounted in theroller assembly relative to the first roller 45 so as to engage thechain 37 as it begins to move laterally along the length of the surfaceof roller 45 in response to the pivoting of the dump body 11 and therotation of the tailgate assembly 27. After the second roller engagesthe chain 37, further pivoting of the dump body 11 will cause the chain37 to angle about the second roller in the X-Z plane. Because the chain37 is biased forward, the first roller 45 is able to hold the chain awayfrom the edge 41 without being of a substantially longer length. Inaddition, by limiting the amount of travel of the chain 37 along thelength of the roller 45, the wear caused by such lateral movement issubstantially reduced. Because the chain no longer catches and releasesin response to the frictional dynamics of the chain moving laterallyover an elongated roller as in the prior art, the raising and loweringof the tailgate assembly 27 in accordance with the invention is muchsmoother than previously possible in tailgate assemblies withoutoutriggers.

Viewing the dump body 11 from the side and in its lowered position asillustrated in FIG. 2, the chain 37 appears as aligned substantially ina straight line. Actually, the chain 37 is angled in the Y-Z plane aboutthe edge 41 by the first roller 45, as best seen in FIG. 3, whose axisof rotation r₁ is in approximate parallel alignment with the edge 41.When the operator of the vehicle activates the hoist cylinders 42, thedump body 11 pivots, thereby causing the roller assembly 43 and thetailgate assembly 27 to rotate about the pivot pin 25a. As the dump body11 pivots toward its dump position shown in FIGS. 4 and 5, the extensionpiece 35 moves relative to the roller assembly 43 and the mountingsupport 39.

Since the chain 37 remains taut as the dump body 11 pivots, it attemptsto maintain a straight line between the extension piece 35 and themounting support 39. In attempting to maintain such a straight line, thechain moves along the length of roller 45 as the relative positions ofthe extension piece 35 and mounting support 39 change. Because roller 47is mounted for rotation about an axis r₂ that is transverse to the axisof rotation r₁ for roller 45, when the chain 37 reaches the surface ofthe roller 47 it is prevented from traveling further along the length ofroller 45, and it is biased by the surface of the roller so thatcontinued pivoting of the dump body 11 causes the chain 37 to rotate theroller as the chain becomes angled in the X-Z plane as well as the Y-Zplane.

Referring to FIG. 6, each of the roller assemblies 43 includes first andsecond metal plates 49 and 50 which are mounted on the edges to thebottom sheet 17 of the truck body 11. At the free ends of the plates 49and 50, metal cross members 51 and 53 brace the plates so as to providea sturdy open box structure. Spanning plates 49 and 50, the journals ofroller 45 are received by holes in the plates which are surrounded bybushings 62 (only one is shown) mounted on the outside surface of eachof the plates. Likewise, roller 47 spans the opposing cross members 51and 53 with its journals being received by holes in each of the crossmembers which are surrounded by bushings 60 mounted on the outsidesurface of the members. To further support the roller assembly 43,struts 65 (only one is shown in FIG. 2) extend from the outside of theplates 49 and 50 to the surface of the bottom sheet 17.

Each of the rollers 45 and 47 is constructed of large and small tubingconcentrically positioned and capped at both ends by a donut-shapedmetal piece. The foregoing construction creates a central bore througheach roller 45,47 that receives an elongated rod that serves as a shaftabout which the rollers rotate. The ends of the shafts serve as thejournals which are received by the bushings 62 and 60. As a possibleaddition to the roller assembly, a layer of rubber may be vulcanized toits circumference in order to further improve the smoothness of themovement of the chain 37 over the surface of the roller.

The extension piece 35, roller assembly 43 and mounting support 39 maybe moved relative to one another from their positions shown in thedrawings in order to provide for varying degrees of tailgate rotationwhich maximizes the opening of the tailgate relative to the body.Because such repositioning may result in the chain 37 rubbing the plate50 of the roller assembly 43, a third roller mounted in the assembly mayprove necessary. By simply extending the length of the cross members 51and 53 and the length of the roller 45, the third roller can be addedwhich is supported by the cross members on the forward side of the chain37. The third roller may have an axis of rotation parallel with the axisof rotation r₂ of the second roller 47.

The chain 37 may be a single continuous chain which reaches from oneextension piece 35 to the other as best shown in FIGS. 3 and 5. For acontinuous chain 37, the mounting 39 is preferably a conduit throughwhich the chain passes. A single continuous chain 37 responds to changesin the tension of the chain on each side of the body resulting fromuneven tilting of the body. If this happens, the distance between theends 39 of the mounting support 39 and the extension pieces 35 willincrease on one side and decrease on the other side. By making the chain37 continuous, any shifting or tilting of the body 11 is compensated forby movement of the chain through the hollow of the support mounting 39.

If the chain 37 breaks, release of the chain's tension on both sides ofthe body can be avoided by limiting the chain's freedom of movementthrough the mounting support 39. For example, a short auxiliary chainmay attach the chain 39 to the mounting support such that a break on oneside will permit only a limited release of the tension on the opposingside because the auxiliary chain will hold the unbroken side to themounting support.

The preferred way of implementing the chains 37 is to provide twoseparate chains whose ends are secured to the ends 39a of the mountingsupport 39 thus tending to stabilize the tilting of the body. In orderto attach the ends of each separate chain 37 to the ends 39a of themounting support, the ends 39a are formed by welding a metal plate (notshown) over each end of the mounting support 39. Two support brackets(not shown) are positioned to be standing on end with the metal plate astheir base. These support brackets receive a nut and bolt assembly thatalso receives the last link of the chain 37. Because the last link issandwiched between the two support brackets, the nut and bolt assemblysecures the end of the chain 37 to the mounting support 39.

Turning to FIGS. 7-15, often tailgate assemblies such as the oneillustrated in FIGS. 1-5 are plagued by a problem of bouncing abouttheir axes of rotation in response to movement of the truck over roughterrain. Sometimes, when the truck body is of a type where the tailgateextends substantially beyond the rear axle of the truck, this bouncingcan be more than merely annoying. In fact, when the moment of thetailgate's center of gravity relative to the rear axle is sufficientlygreat, even small jolts to the axle from rough roads may cause thebouncing of the tailgate to be sufficiently severe that repeated travelover the rough roads will quickly damage the tailgate and body. In suchsituations, it is known to include cushioning materials on the surfacesupon which the tailgate rests in its lowered position in order to dampenout the bouncing of the tailgate assembly. Although this "solution"makes the bouncing less annoying and helps prevent serious damage to thetailgate assembly or the truck body, it does not address the underlyingproblem of bouncing caused by the moment of rotation generated by thejolting of the truck as it moves over rough hauling roads.

Referring specifically to FIGS. 7-9, a tailgate assembly 51 includes twoside panels 53 (only one of which is shown in FIG. 7) and a rear panel55 for providing a back wall of the dump body 13 when the body is itslowered position as shown in FIG. 7. Inasmuch as only one side panel 53is illustrated by the side views of FIGS. 7-9, only one side will bedescribed in detail; but it will be understood that identical structureand function are associated with the side panel not shown.

In accordance with one important aspect of the invention, rotation ofthe dump body 11 toward its fully-raised position causes a compoundaction of sequentially: 1) unlocking back panel 55; 2) rotating the sidepanels 53 against gravity and about axis 59; and 3) rotating the backpanels 55 against gravity about axis 67. This sequential action causesthe compound rotation of the back panel 55 and side panels 53. Thismechanically effectuated rotation of back panel 55 effectively increasesthe gate-to-body clearance. A detailed description of the means forcreating this compound action is discussed below.

An extension portion of each side panel 53 of the tailgate assembly 51extends forward of an axis of rotation 59 and includes an anchor 61 fora chain 63 connecting the extension portion 57 to the frame 23 of thetruck at the mounting support 39 by way of the roller assemblies 43. Inits lowered position, the side panel 53 of the tailgate assembly 51rests upon platform 65 mounted to the side sheet 13. It is theseplatforms that are typically provided with cushioning material to softenthe blows to the body 13 caused by bouncing of the tailgate assembly 51.The back panel 55 of the tailgate assembly 51 is mounted between the twoopposing and parallel side panels 53 so as to be rotatable about an axis67.

The tailgate assembly 51 includes a means for locking the back panel 55into a fixed position relative to the side panels 53 when the tailgateassembly is in its fully lowered position as shown in FIG. 7 so that inconjunction with the locked position of the back panel 55, the entiretailgate assembly 51 is locked to the dump body 11 so as to preventbouncing. The chain 63 is incorporated into a mechanism that responds torotation of the dump body 11 about its pivot point 25a such that thelocking means in the tailgate assembly first releases the back panel 55for rotation about pivot axis 67. Such rotation causes the entiretailgate assembly 51 to be released from locked engagement with the dumpbody 11 so that continued rotation of the dump body to its fully raisedposition will allow the tailgate assembly to respond by rotating aboutits axis 59.

Referring to FIG. 7 in conjunction with FIG. 10, the locking meansaccording to a preferred embodiment of the invention includes a bellcrank 69 mounted to a pivot pin 71 defining the pivot axis 67 of theback panel 55. Attached to one projection 69a of the bell crank 69, is afirst end of a chain extension 72 that extends from the bell crank to ajunction 73 joining the chain 63 at an intermediate point so as tocreate a short link 63a extending from the anchor 61. This three-pointsuspension or Y-configuration of the inter-connected chains 63, 63a and72 allows the interaction of the chains to provide the appropriate forceon the bell crank 69 in response to rotation of the dump body 11.Specifically, as can be appreciated by comparing the position of thechains 63, 63a and 72 in FIGS. 7 and 8, initial rotation of the dumpbody 11 first causes the chain sections 63 and 63a to align withouteffecting rotation of the side panels 53. But, as a result of thealignment of the chain sections 63 and 63 a, the chain section 72 ismoved forward as indicated by the arrow 75 in FIG. 8.

Longitudinal movement of the chain section 72 in the forward directioncauses the bell crank 69 to rotate counter-clockwise as indicated inFIG. 11 and, as a result, an elongated shaft 77 secured to a secondprojection 69b of the bell crank is moved upwardly along thelongitudinal axis of the shaft.

In the rest position of the shaft 77 illustrated in FIG. 10, thelowermost end 77a of the shaft 77 extends in front of a stop 79 mountedto the side panel 53 of the tailgate assembly 51. The shaft 77 ismounted to the back panel 55 of the tailgate assembly 51 by way of a topbracket member 81 and a bottom bracket member 83 that are both rigidlysecured to the inside wall of the back panel. By locating the stop 79relative to the rest or locking position of the shaft 77 as illustratedin FIGS. 10 and 13, any attempted rotation of the back panel 55 causesengagement of the stop 79 with the lowermost end 77a of the shaft 77.Thus, the back panel 53 cannot rotate when the shaft 77 is in its restposition. Each of the brackets 81 and 83, include central openings thatfreely receive the body of the shaft 77.

The cut away view of the locking mechanism shown in FIG. 13 more clearlyillustrates the construction of the mechanisms associated with theelongated shaft 77 and the interaction of the lowermost extension 77a ofthe shaft with the stop 79. In order to bias the shaft 77 in its rest orlocking position, a coiled spring 85 is fitted over the elongated shaft77 and is held between the first bracketing member 81 and a pair ofthreaded nuts 87 mounted to the shaft and including a washer 89 thatserves as a base or platform for the spring. As the dump body 11 israised, the chain 72 moves forward, the bell crank 69 rotates, the shaft77 is lifted and the spring 85 is compressed. Upon lowering of the dumpbody 11, the compressed spring 85 will force the shaft 77 to extenddownwardly and lock the back panel 55 to the side panels 53. In order toallow the bell crank 69 to pivot relative to the uppermost end of theshaft 77, a bracketing member 91 spans the distance between the top ofthe shaft 77 and the bell crank portion 69b.

Rotation of the dump body 11 toward its fully raised position causes astop 93 to engage an extension 95 (as seen in FIGS. 11,12) that issecured to the inner wall of the back panel 55. As the dump body 11continues to rotate toward its fully raised position, the engagement ofthe stop 93 with the extension 95 results in rotation of the back panel55 in response to further rotation of the bell crank 69 and the dumpbody. Because of the three-point suspension of the chain 63, 63a and 72,the forward movement of the chain 72 will become less responsive torotation of the dump body 11 as the tailgate assembly 51 moves the chainsection 72 more closely into a linear alignment with the chain section63a.

In order to lock the tailgate assembly 51 to the dump body 13, a flange96 is mounted to a protruding member 97 of the back panel 55 forengagement with a complementary flange 99 mounted to the back edge ofthe dump body 11. As can be seen from FIGS. 10, 11 and 12, the tailgateassembly 51 is prevented from freely rotating relative to the dump body11 by the engagement of the complementary flanges 96 and 99.Furthermore, the platform 65 (shown in FIGS. 7-9) defines the restingposition for the tailgate assembly 51 relative to the dump body 11 sothat there is virtually no play between the tailgate assembly and thedump body when the flanges 96 and 99 are engaged. As a safety feature,the flange 96 mounted to the protruding member 97 includes two mountingpins 101 and 103. Pin 101 is intended as a shear pin so that failure ofproper operation of the locking mechanism upon rotation of the dumpbody, will only result in the shearing of the shear pin and, as aresult, the rotation of the flange 96 about pin 103 so as to swing theflange away from the flange 99 and thereby free the tailgate assembly 51for rotation.

Referring to FIGS. 14 and 15, the locking mechanism generally indicatedas 105 in FIG. 14, is mounted inside a hollow area defined by theopposing metal sheets forming each side panel 53 of the tailgateassembly 51. In order to protect the locking mechanism 105 fromcontamination by dust, dirt and rocks, a protective cover plate 107 ismounted over the locking mechanism in order to close an opening 109 (seeFIG. 13) in the top of the side panel 53 for allowing access to thelocking mechanism 105. In order for the protective cover 107 tocooperate with the rotating of the back panel 55, the cover is hinged tothe back panel at hinge assembly 111 best seen in FIGS. 10-13.

The protective cover 107 is characterized by an inverted"U"-cross-sectional shape that fits over the top of the side panel 53and includes a slot 107a on the side of each of the side walls of theprotective cover. The recess 107a receives a pin 113 in order to supportthe protective cover 107 on the side panel 53. Rotation of the backpanel 55 causes the protective cover 107 to move forward following themotion dictated to it by the interaction of the slot 107a and the pin113, thereby providing for easy forward and backward movement of theprotective cover in response to rotation of the back panel 55.

From the foregoing, it will be appreciated that the connecting mechanismof the invention provides an effective means for raising and lowering atailgate assembly for heavy-duty, off-road trucks without necessitatingthe use of an outrigger. Furthermore, the dual-roller assembly 43 allowsthe chain 37 or 63 to easily move relative to the dump body 11 withoutjumping and without requiring cumbersome accessory equipment in lieu ofoutriggers. Also, the particular tailgate assembly 51 illustrated inFIGS. 7-15 cooperates with the connecting mechanism so as to provide atailgate assembly that is free of the damaging effects caused bybouncing of the tailgate assembly in response to jolting of the truck asit travels over rough roads.

We claim:
 1. An apparatus for securing and locking a tailgate assemblywith a dump body, the dump body having a bottom sheet, two side sheets,and a front sheet for carrying a load and pivotally mounted on a truckframe for rotation about a first axis between load and dump positions,the apparatus comprising:a tailgate assembly pivotally mounted to thedump body for movement between the load and dump positions andcomprising two opposing and parallel side panels having first and secondends, the first ends are pivotally mounted to the side sheets of thedump body for rotation about a second axis of rotation, a back panelspanning the distance between the second ends of the side panels andforming a rear wall of the dump body is pivotally mounted to the secondends of the side panels for rotation about a third axis which issubstantially parallel to the first and second axes; a lift for rotatingthe dump body about the first axis between the load and dump positions;a continuous linkage having first and second portions wherein the firstportion is connected between the frame and the side panels of thetailgate assembly to rotate the tailgate assembly in response torotation of the dump body between the load and dump positions and thesecond portion is connected between the first portion and the back panelto rotate the back panel in response to rotation of the dump bodybetween the load and dump positions and during rotation of the tailgateassembly, the linkage comprises at least one three-section chainconnected in a Y-configuration wherein the chain has three ends with afirst end anchored to the frame, a second end anchored to at least oneof the side panels and a third end anchored to the lock; and a locksupported by the back panel and movable between a first positionpreventing the back panel from rotating about the third axis and asecond position permitting the back panel to rotate about the thirdaxis.
 2. An apparatus as set forth in claim 1 wherein the back panelincludes a flange extending from a lowermost portion of the back paneland mating in locked engagement with a flange extending from the bodysuch that the flanges are in the locked engagement when the dump body isin its lowered position, thereby preventing any undesired rotation ofthe tailgate assembly caused by torques created by jolting of the truckframe.
 3. An apparatus as set forth in claim 2 wherein rotation of theback panel by the linkage disengages the flanges and frees the tailgateassembly for rotation about the third axis of rotation.
 4. An apparatusas set forth in claim 1 wherein the dump body includes a bottom sheetmeeting each of the two side walls at a junction forming an edge, theapparatus further comprising;at least one pair of roller assemblies eachmounted on the dump body adjacent one of the edges; one section of thechain comprising the linkage joining the tailgate assembly to the framewhereby the one section is biased away from the edges by the associatedroller assembly in a manner so as to create angles in the one sectionthat lie approximately in a first plane that is substantially transverseto a second plane, which is substantially parallel with the side walls;the one section responding to the pivoting of the dump body bygenerating a torque on the tailgate assembly, thereby causing rotationof the tailgate assembly about the third axis of rotation; and each ofthe roller assemblies including means for angling the one section in thesecond plane in addition to the first plane as the body pivots and thetailgate assembly rotates so that the one section is biased along thelength of the associated edge by the angling means to limitrepositioning of the linkage along the length of the edge as the bodypivots and the tailgate assembly rotates.
 5. An apparatus as set forthin claim 4 wherein each of the roller assemblies comprises:a firstcylindrical roller mounted in the assembly for rotation about a fourthaxis substantially parallel with the associated edge, the first rollerbiasing the one section so as to be angled in the first plane; and themeans for angling the one section in the second plane comprising asecond cylindrical roller mounted in the assembly for rotation about afifth axis substantially transverse to the fourth axis, the secondroller biasing the one section so as to be angled in the second plane.